Power supply for a subcutaneous implantable cardioverter-defibrillator

ABSTRACT

A power supply for an implantable cardioverter-defibrillator for subcutaneous positioning between the third rib and the twelfth rib and for providing cardioversion/defibrillation energy to the heart, the power supply comprising a capacitor subsystem for storing the cardioversion/defibrillation energy for delivery to the patient&#39;s heart; and a battery subsystem electrically coupled to the capacitor subsystem for providing electrical energy to the capacitor subsystem.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication entitled “SUBCUTANEOUS ONLY IMPLANTABLECARDIOVERTER-DEFIBRILLATOR AND OPTIONAL PACER,” having Ser. No.09/663,607, filed Sep. 18, 2000, pending, U.S. patent applicationentitled “UNITARY SUBCUTANEOUS ONLY IMPLANTABLECARDIOVERTER-DEFIBRILLATOR AND OPTIONAL PACER,” having Ser. No.09/663,606, filed Sep. 18, 2000, pending, and U.S. patent applicationentitled “POWER SUPPLY FOR AN IMPLANTABLE SUBCUTANEOUSCARDIOVERTER-DEFIBRILLATOR,” filed Aug. 27, 2001, pending, of which allapplications are assigned to the assignee of the present application,and the disclosures of all applications are hereby incorporated byreference.

FIELD OF THE INVENTION

Method for performing electrical cardioversion/defibrillation andoptional pacing of the heart via a totally subcutaneous non-transvenoussystem.

BACKGROUND OF THE INVENTION

Defibrillation/cardioversion is a technique employed to counterarrhythmic heart conditions including some tachycardias in the atriaand/or ventricles. Typically, electrodes are employed to stimulate theheart with electrical impulses or shocks, of a magnitude substantiallygreater than pulses used in cardiac pacing. Shocks used fordefibrillation therapy can comprise a biphasic truncated exponentialwaveform. As for pacing, a constant current density is desired to reduceor eliminate variability due to the electrode/tissue interface.

Defibrillation/cardioversion systems include body implantable electrodesthat are connected to a hermetically sealed container housing theelectronics, battery supply and capacitors. The entire system isreferred to as implantable cardioverter/defibrillators (ICDs). Theelectrodes used in ICDs can be in the form of patches applied directlyto epicardial tissue, or, more commonly, are on the distal regions ofsmall cylindrical insulated catheters that typically enter thesubclavian venous system, pass through the superior vena cava and intoone or more endocardial areas of the heart. Such electrode systems arecalled intravascular or transvenous electrodes. U.S. Pat. Nos.4,603,705, 4,693,253, 4,944,300, 5,105,810, the disclosures of which areall incorporated herein by reference, disclose intravascular ortransvenous electrodes, employed either alone, in combination with otherintravascular or transvenous electrodes, or in combination with anepicardial patch or subcutaneous electrodes. Compliant epicardialdefibrillator electrodes are disclosed in U.S. Pat. Nos. 4,567,900 and5,618,287, the disclosures of which are incorporated herein byreference. A sensing epicardial electrode configuration is disclosed inU.S. Pat. No. 5,476,503, the disclosure of which is incorporated hereinby reference.

In addition to epicardial and transvenous electrodes, subcutaneouselectrode systems have also been developed. For example, U.S. Pat. Nos.5,342,407 and 5,603,732, the disclosures of which are incorporatedherein by reference, teach the use of a pulse monitor/generatorsurgically implanted into the abdomen and subcutaneous electrodesimplanted in the thorax. This system is far more complicated to use thancurrent ICD systems using transvenous lead systems together with anactive can electrode and therefore it has no practical use. It has infact never been used because of the surgical difficulty of applying sucha device (3 incisions), the impractical abdominal location of thegenerator and the electrically poor sensing and defibrillation aspectsof such a system.

Recent efforts to improve the efficiency of ICDs have led manufacturersto produce ICDs which are small enough to be implanted in the pectoralregion. In addition, advances in circuit design have enabled the housingof the ICD to form a subcutaneous electrode. Some examples of ICDs inwhich the housing of the ICD serves as an optional additional electrodeare described in U.S. Pat. Nos. 5,133,353, 5,261,400, 5,620,477, and5,658,321 the disclosures of which are incorporated herein by reference.

ICDs are now an established therapy for the management of lifethreatening cardiac rhythm disorders, primarily ventricular fibrillation(V-Fib). ICDs are very effective at treating V-Fib, but are therapiesthat still require significant surgery.

As ICD therapy becomes more prophylactic in nature and used inprogressively less ill individuals, especially children at risk ofcardiac arrest, the requirement of ICD therapy to use intravenouscatheters and transvenous leads is an impediment to very long termmanagement as most individuals will begin to develop complicationsrelated to lead system malfunction sometime in the 5-10 year time frame,often earlier. In addition, chronic transvenous lead systems, theirreimplantation and removals, can damage major cardiovascular venoussystems and the tricuspid valve, as well as result in life threateningperforations of the great vessels and heart. Consequently, use oftransvenous lead systems, despite their many advantages, are not withouttheir chronic patient management limitations in those with lifeexpectancies of >5 years. The problem of lead complications is evengreater in children where body growth can substantially altertransvenous lead function and lead to additional cardiovascular problemsand revisions. Moreover, transvenous ICD systems also increase cost andrequire specialized interventional rooms and equipment as well asspecial skill for insertion. These systems are typically implanted bycardiac electrophysiologists who have had a great deal of extratraining.

In addition to the background related to ICD therapy, the presentinvention requires a brief understanding of a related therapy, theautomatic external defibrillator (AED). AEDs employ the use of cutaneouspatch electrodes, rather than implantable lead systems, to effectdefibrillation under the direction of a bystander user who treats thepatient suffering from V-Fib with a portable device containing thenecessary electronics and power supply that allows defibrillation. AEDscan be nearly as effective as an ICD for defibrillation if applied tothe victim of ventricular fibrillation promptly, i.e., within 2 to 3minutes of the onset of the ventricular fibrillation.

AED therapy has great appeal as a tool for diminishing the risk of deathin public venues such as in air flight. However, an AED must be used byanother individual, not the person suffering from the potential fatalrhythm. It is more of a public health tool than a patient-specific toollike an ICD. Because >75% of cardiac arrests occur in the home, and overhalf occur in the bedroom, patients at risk of cardiac arrest are oftenalone or asleep and can not be helped in time with an AED. Moreover, itssuccess depends to a reasonable degree on an acceptable level of skilland calm by the bystander user.

What is needed therefore, especially for children and for prophylacticlong term use for those at risk of cardiac arrest, is a combination ofthe two forms of therapy which would provide prompt and near-certaindefibrillation, like an ICD, but without the long-term adverse sequelaeof a transvenous lead system while simultaneously using most of thesimpler and lower cost technology of an AED. What is also needed is acardioverter/defibrillator that is of simple design and can becomfortably implanted in a patient for many years.

SUMMARY OF THE INVENTION

A power supply for an implantable cardioverter-defibrillator forsubcutaneous positioning between the third rib and the twelfth rib andfor providing cardioversion/defibrillation energy to the heart, thepower supply comprising a capacitor subsystem for storing thecardioversion/defibrillation energy for delivery to the patient's heart;and a battery subsystem electrically coupled to the capacitor subsystemfor providing electrical energy to the capacitor subsystem.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, reference is now made tothe drawings where like numerals represent similar objects throughoutthe figures where:

FIG. 1 is a schematic view of a Subcutaneous ICD (S-ICD) of the presentinvention;

FIG. 2 is a schematic view of an alternate embodiment of a subcutaneouselectrode of the present invention;

FIG. 3 is a schematic view of an alternate embodiment of a subcutaneouselectrode of the present invention;

FIG. 4 is a schematic view of the S-ICD and lead of FIG. 1subcutaneously implanted in the thorax of a patient;

FIG. 5 is a schematic view of the S-ICD and lead of FIG. 2subcutaneously implanted in an alternate location within the thorax of apatient;

FIG. 6 is a schematic view of the S-ICD and lead of FIG. 3subcutaneously implanted in the thorax of a patient;

FIG. 7 is a schematic view of the method of making a subcutaneous pathfrom the preferred incision and housing implantation point to atermination point for locating a subcutaneous electrode of the presentinvention;

FIG. 8 is a schematic view of an introducer set for performing themethod of lead insertion of any of the described embodiments;

FIG. 9 is a schematic view of an alternative S-ICD of the presentinvention illustrating a lead subcutaneously and serpiginously implantedin the thorax of a patient for use particularly in children;

FIG. 10 is a schematic view of an alternate embodiment of an S-ICD ofthe present invention;

FIG. 11 is a schematic view of the S-ICD of FIG. 10 subcutaneouslyimplanted in the thorax of a patient;

FIG. 12 is a schematic view of yet a further embodiment where thecanister of the S-ICD of the present invention is shaped to beparticularly useful in placing subcutaneously adjacent and parallel to arib of a patient; and

FIG. 13 is a schematic of a different embodiment where the canister ofthe S-ICD of the present invention is shaped to be particularly usefulin placing subcutaneously adjacent and parallel to a rib of a patient.

FIG. 14 is a schematic view of a Unitary Subcutaneous ICD (US-ICD) ofthe present invention;

FIG. 15 is a schematic view of the US-ICD subcutaneously implanted inthe thorax of a patient;

FIG. 16 is a schematic view of the method of making a subcutaneous pathfrom the preferred incision for implanting the US-ICD.

FIG. 17 is a schematic view of an introducer for performing the methodof US-ICD implantation; and

FIG. 18 is an exploded schematic view of an alternate embodiment of thepresent invention with a plug-in portion that contains operationalcircuitry and means for generating cardioversion/defibrillation shockwaves.

FIG. 19 is a block diagram showing the power supply of an implantablecardioverter/defibrillator in an embodiment according to the presentinvention.

FIG. 20 is a table that shows several examples of embodiments of thepresent invention comprising various numbers of capacitors and pulsewidths.

FIG. 21 is a graph that shows several examples of embodiments of thepresent invention comprising various numbers of capacitors and pulsewidths.

FIG. 22 is a table that shows several examples for the battery subsystemcomprising two battery cells, as well as varying efficiencies and chargetimes in an embodiment of the present invention.

FIG. 23 is a table that shows several examples for the battery subsystemcomprising various numbers of battery cells, efficiencies and chargetimes in an embodiment of the present invention.

FIG. 24 is a diagram that shows one example of a physical layout for thebattery subsystem and the capacitor subsystem in an embodiment of thepresent invention.

FIG. 25 shows one example of a physical layout for the battery subsystem102 and the capacitor subsystem 104 in an embodiment of the presentinvention.

FIG. 26 is a table that shows various examples of sizes for the combinedcapacitor subsystem and the battery subsystem in an embodiment of thepresent invention.

FIG. 27 is a table that shows several examples of the capacitorsubsystem and the battery subsystem at different energy levels in anembodiment of the present invention.

DETAILED DESCRIPTION

Turning now to FIG. 1, the S-ICD of the present invention isillustrated. The S-ICD consists of an electrically active canister 11and a subcutaneous electrode 13 attached to the canister. The canisterhas an electrically active surface 15 that is electrically insulatedfrom the electrode connector block 17 and the canister housing 16 viainsulating area 14. The canister can be similar to numerous electricallyactive canisters commercially available in that the canister willcontain a battery supply, capacitor and operational circuitry.Alternatively, the canister can be thin and elongated to conform to theintercostal space. The circuitry will be able to monitor cardiac rhythmsfor tachycardia and fibrillation, and if detected, will initiatecharging the capacitor and then delivering cardioversion /defibrillationenergy through the active surface of the housing and to the subcutaneouselectrode. Examples of such circuitry are described in U.S. Pat. Nos.4,693,253 and 5,105,810, the entire disclosures of which are hereinincorporated by reference. The canister circuitry can providecardioversion/ defibrillation energy in different types of waveforms. Inone embodiment, a 100 uF biphasic waveform is used of approximately10-20 ms total duration and with the initial phase containingapproximately ⅔ of the energy, however, any type of waveform can beutilized such as monophasic, biphasic, multiphasic or alternativewaveforms as is known in the art.

In addition to providing cardioversion/ defibrillation energy, thecircuitry can also provide transthoracic cardiac pacing energy. Theoptional circuitry will be able to monitor the heart for bradycardiaand/or tachycardia rhythms. Once a bradycardia or tachycardia rhythm isdetected, the circuitry can then deliver appropriate pacing energy atappropriate intervals through the active surface and the subcutaneouselectrode. Pacing stimuli will be biphasic in one embodiment and similarin pulse amplitude to that used for conventional transthoracic pacing.

This same circuitry can also be used to deliver low amplitude shocks onthe T-wave for induction of ventricular fibrillation for testing S-ICDperformance in treating V-Fib as is described in U.S. Pat. No.5,129,392, the entire disclosure of which is hereby incorporated byreference. Also the circuitry can be provided with rapid induction ofventricular fibrillation or ventricular tachycardia using rapidventricular pacing. Another optional way for inducing ventricularfibrillation would be to provide a continuous low voltage, i.e., about 3volts, across the heart during the entire cardiac cycle.

Another optional aspect of the present invention is that the operationalcircuitry can detect the presence of atrial fibrillation as described inOlson, W. et al. “Onset And Stability For Ventricular TachyarrhythmiaDetection in an Implantable Cardioverter and Defibrillator,” Computersin Cardiology (1986) pp. 167-170. Detection can be provided via R-RCycle length instability detection algorithms. Once atrial fibrillationhas been detected, the operational circuitry will then provide QRSsynchronized atrial defibrillation/cardioversion using the same shockenergy and waveshape characteristics used for ventriculardefibrillation/ cardioversion.

The sensing circuitry will utilize the electronic signals generated fromthe heart and will primarily detect QRS waves. In one embodiment, thecircuitry will be programmed to detect only ventricular tachycardias orfibrillations. The detection circuitry will utilize in its most directform, a rate detection algorithm that triggers charging of the capacitoronce the ventricular rate exceeds some predetermined level for a fixedperiod of time: for example, if the ventricular rate exceeds 240 bpm onaverage for more than 4 seconds. Once the capacitor is charged, aconfirmatory rhythm check would ensure that the rate persists for atleast another 1 second before discharge. Similarly, terminationalgorithms could be instituted that ensure that a rhythm less than 240bpm persisting for at least 4 seconds before the capacitor charge isdrained to an internal resistor. Detection, confirmation and terminationalgorithms as are described above and in the art can be modulated toincrease sensitivity and specificity by examining QRS beat-to-beatuniformity, QRS signal frequency content, R-R interval stability data,and signal amplitude characteristics all or part of which can be used toincrease or decrease both sensitivity and specificity of S-ICDarrhythmia detection function.

In addition to use of the sense circuitry for detection of V-Fib orV-Tach by examining the QRS waves, the sense circuitry can check for thepresence or the absence of respiration. The respiration rate can bedetected by monitoring the impedance across the thorax usingsubthreshold currents delivered across the active can and the highvoltage subcutaneous lead electrode and monitoring the frequency inundulation in the waveform that results from the undulations oftransthoracic impedance during the respiratory cycle. If there is noundulation, then the patent is not respiring and this lack ofrespiration can be used to confirm the QRS findings of cardiac arrest.The same technique can be used to provide information about therespiratory rate or estimate cardiac output as described in U.S. Pat.Nos. 6,095,987, 5,423,326, 4,450,527, the entire disclosures of whichare incorporated herein by reference.

The canister of the present invention can be made out of titanium alloyor other presently preferred electrically active canister designs.However, it is contemplated that a malleable canister that can conformto the curvature of the patient's chest will be preferred. In this waythe patient can have a comfortable canister that conforms to the shapeof the patient's rib cage. Examples of conforming canisters are providedin U.S. Pat. No. 5,645,586, the entire disclosure of which is hereinincorporated by reference. Therefore, the canister can be made out ofnumerous materials such as medical grade plastics, metals, and alloys.In the preferred embodiment, the canister is smaller than 60 cc volumehaving a weight of less than 100 gms for long term wearability,especially in children. The canister and the lead of the S-ICD can alsouse fractal or wrinkled surfaces to increase surface area to improvedefibrillation capability. Because of the primary prevention role of thetherapy and the likely need to reach energies over 40 Joules, a featureof the preferred embodiment is that the charge time for the therapy,intentionally e relatively long to allow capacitor charging within thelimitations of device size. Examples of small ICD housings are disclosedin U.S. Pat. Nos. 5,597,956 and 5,405,363, the entire disclosures ofwhich are herein incorporated by reference.

Different subcutaneous electrodes 13 of the present invention areillustrated in FIGS. 1-3. Turning to FIG. 1, the lead 21 for thesubcutaneous electrode is preferably composed of silicone orpolyurethane insulation. The electrode is connected to the canister atits proximal end via connection port 19 which is located on anelectrically insulated area 17 of the canister. The electrodeillustrated is a composite electrode with three different electrodesattached to the lead. In the embodiment illustrated, an optional anchorsegment 52 is attached at the most distal end of the subcutaneouselectrode for anchoring the electrode into soft tissue such that theelectrode does not dislodge after implantation.

The most distal electrode on the composite subcutaneous electrode is acoil electrode 27 that is used for delivering the high voltagecardioversion/defibrillation energy across the heart. The coilcardioversion/defibrillation electrode is about 5-10 cm in length.Proximal to the coil electrode are two sense electrodes, a first senseelectrode 25 is located proximally to the coil electrode and a secondsense electrode 23 is located proximally to the first sense electrode.The sense electrodes are spaced far enough apart to be able to have goodQRS detection. This spacing can range from 1 to 10 cm with 4 cm beingpresently preferred. The electrodes may or may not be circumferentialwith the preferred embodiment. Having the electrodes non-circumferentialand positioned outward, toward the skin surface, is a means to minimizemuscle artifact and enhance QRS signal quality. The sensing electrodesare electrically isolated from the cardioversion/defibrillationelectrode via insulating areas 29. Similar types ofcardioversion/defibrillation electrodes are currently commerciallyavailable in a transvenous configuration. For example, U.S. Pat. No.5,534,022, the entire disclosure of which is herein incorporated byreference, disclosures a composite electrode with a coilcardioversion/defibrillation electrode and sense electrodes.Modifications to this arrangement is contemplated within the scope ofthe invention. One such modification is illustrated in FIG. 2 where thetwo sensing electrodes 25 and 23 are non-circumferential sensingelectrodes and one is located at the distal end, the other is locatedproximal thereto with the coil electrode located in between the twosensing electrodes. In this embodiment the sense electrodes are spacedabout 6 to about 12 cm apart depending on the length of the coilelectrode used. FIG. 3 illustrates yet a further embodiment where thetwo sensing electrodes are located at the distal end to the compositeelectrode with the coil electrode located proximally thereto. Otherpossibilities exist and are contemplated within the present invention.For example, having only one sensing electrode, either proximal ordistal to the coil cardioversion/defibrillation electrode with the coilserving as both a sensing electrode and a cardioversion/defibrillationelectrode.

It is also contemplated within the scope of the invention that thesensing of QRS waves (and transthoracic impedance) can be carried outvia sense electrodes on the canister housing or in combination with thecardioversion/defibrillation coil electrode and/or the subcutaneous leadsensing electrode(s). In this way, sensing could be performed via theone coil electrode located on the subcutaneous electrode and the activesurface on the canister housing. Another possibility would be to haveonly one sense electrode located on the subcutaneous electrode and thesensing would be performed by that one electrode and either the coilelectrode on the subcutaneous electrode or by the active surface of thecanister. The use of sensing electrodes on the canister would eliminatethe need for sensing electrodes on the subcutaneous electrode. It isalso contemplated that the subcutaneous electrode would be provided withat least one sense electrode, the canister with at least one senseelectrode, and if multiple sense electrodes are used on either thesubcutaneous electrode and/or the canister, that the best QRS wavedetection combination will be identified when the S-ICD is implanted andthis combination can be selected, activating the best sensingarrangement from all the existing sensing possibilities. Turning againto FIG. 2, two sensing electrodes 26 and 28 are located on theelectrically active surface 15 with electrical insulator rings 30 placedbetween the sense electrodes and the active surface. These canistersense electrodes could be switched off and electrically insulated duringand shortly after defibrillation/cardioversion shock delivery. Thecanister sense electrodes may also be placed on the electricallyinactive surface of the canister. In the embodiment of FIG. 2, there areactually four sensing electrodes, two on the subcutaneous lead and twoon the canister. In the preferred embodiment, the ability to changewhich electrodes are used for sensing would be a programmable feature ofthe S-ICD to adapt to changes in the patient physiology and size (in thecase of children) over time. The programming could be done via the useof physical switches on the canister, or as presently preferred, via theuse of a programming wand or via a wireless connection to program thecircuitry within the canister.

The canister could be employed as either a cathode or an anode of theS-ICD cardioversion/defibrillation system. If the canister is thecathode, then the subcutaneous coil electrode would be the anode.Likewise, if the canister is the anode, then the subcutaneous electrodewould be the cathode.

The active canister housing will provide energy and voltage intermediateto that available with ICDs and most AEDs. The typical maximum voltagenecessary for ICDs using most biphasic waveforms is approximately 750Volts with an associated maximum energy of approximately 40 Joules. Thetypical maximum voltage necessary for AEDs is approximately 2000-5000Volts with an associated maximum energy of approximately 200-360 Joulesdepending upon the model and waveform used. The S-ICD of the presentinvention uses maximum voltages in the range of about 350 to about 3500Volts and is associated with energies of about 0.5 to about 350 Joules.The capacitance of the S-ICD could range from about 25 to about 200micro farads.

The sense circuitry contained within the canister is highly sensitiveand specific for the presence or absence of life threatening ventriculararrhythmias. Features of the detection algorithm are programmable andthe algorithm is focused on the detection of V-FIB and high rate V-TACH(>240 bpm). Although the S-ICD of the present invention may rarely beused for an actual life threatening event, the simplicity of design andimplementation allows it to be employed in large populations of patientsat modest risk with modest cost by non-cardiac electrophysiologists.Consequently, the S-ICD of the present invention focuses mostly on thedetection and therapy of the most malignant rhythm disorders. As part ofthe detection algorithm's applicability to children, the upper raterange is programmable upward for use in children, known to have rapidsupraventricular tachycardias and more rapid ventricular fibrillation.Energy levels also are programmable downward in order to allow treatmentof neonates and infants.

Turning now to FIG. 4, the optimal subcutaneous placement of the S-ICDof the present invention is illustrated. As would be evidence to aperson skilled in the art, the actual location of the S-ICD is in asubcutaneous space that is developed during the implantation process.The heart is not exposed during this process and the heart isschematically illustrated in the figures only for help in understandingwhere the canister and coil electrode are three dimensionally located inthe left mid-clavicular line approximately at the level of theinframammary crease at approximately the 5th rib. The lead 21 of thesubcutaneous electrode traverses in a subcutaneous path around thethorax terminating with its distal electrode end at the posterioraxillary line ideally just lateral to the left scapula. This way thecanister and subcutaneous cardioversion/defibrillation electrode providea reasonably good pathway for current delivery to the majority of theventricular myocardium.

FIG. 5 illustrates a different placement of the present invention. TheS-ICD canister with the active housing is located in the left posterioraxillary line approximately lateral to the tip of the inferior portionof the scapula. This location is especially useful in children. The lead21 of the subcutaneous electrode traverses in a subcutaneous path aroundthe thorax terminating with its distal electrode end at the anteriorprecordial region, ideally in the inframammary crease. FIG. 6illustrates the embodiment of FIG. 1 subcutaneously implanted in thethorax with the proximal sense electrodes 23 and 25 located atapproximately the left axillary line with thecardioversion/defibrillation electrode just lateral to the tip of theinferior portion of the scapula.

FIG. 7 schematically illustrates the method for implanting the S-ICD ofthe present invention. An incision 31 is made in the left anterioraxillary line approximately at the level of the cardiac apex. Thisincision location is distinct from that chosen for S-ICD placement andis selected specifically to allow both canister location more mediallyin the left inframammary crease and lead positioning more posteriorlyvia the introducer set (described below) around to the left posterioraxillary line lateral to the left scapula. That said, the incision couldbe anywhere on the thorax deemed reasonably by the implanting physicianalthough in the preferred embodiment, the S-ICD of the present inventionwill be applied in this region. A subcutaneous pathway 33 is thencreated medially to the inframmary crease for the canister andposteriorly to the left posterior axillary line lateral to the leftscapula for the lead.

The S-ICD canister 11 is then placed subcutaneously at the location ofthe incision or medially at the subcutaneous region at the leftinframmary crease. The subcutaneous electrode 13 is placed with aspecially designed curved introducer set 40 (see FIG. 8). The introducerset comprises a curved trocar 42 and a stiff curved peel away sheath 44.The peel away sheath is curved to allow for placement around the ribcage of the patient in the subcutaneous space created by the trocar. Thesheath has to be stiff enough to allow for the placement of theelectrodes without the sheath collapsing or bending. Preferably thesheath is made out of a biocompatible plastic material and is perforatedalong its axial length to allow for it to split apart into two sections.The trocar has a proximal handle 41 and a curved shaft 43. The distalend 45 of the trocar is tapered to allow for dissection of asubcutaneous path 33 in the patient. Preferably, the trocar iscannulated having a central Lumen 46 and terminating in an opening 48 atthe distal end. Local anesthetic such as lidocaine can be delivered, ifnecessary, through the lumen or through a curved and elongated needledesigned to anesthetize the path to be used for trocar insertion shouldgeneral anesthesia not be employed. The curved peel away sheath 44 has aproximal pull tab 49 for breaking the sheath into two halves along itsaxial shaft 47. The sheath is placed over a guidewire inserted throughthe trocar after the subcutaneous path has been created. Thesubcutaneous pathway is then developed until it terminatessubcutaneously at a location that, if a straight line were drawn fromthe canister location to the path termination point the line wouldintersect a substantial portion of the left ventricular mass of thepatient. The guidewire is then removed leaving the peel away sheath. Thesubcutaneous lead system is then inserted through the sheath until it isin the proper location. Once the subcutaneous lead system is in theproper location, the sheath is split in half using the pull tab 49 andremoved. If more than one subcutaneous electrode is being used, a newcurved peel away sheath can be used for each subcutaneous electrode.

The S-ICD will have prophylactic use in adults where chronictransvenous/epicardial ICD lead systems pose excessive risk or havealready resulted in difficulty, such as sepsis or lead fractures. It isalso contemplated that a major use of the S-ICD system of the presentinvention will be for prophylactic use in children who are at risk forhaving fatal arrhythmias, where chronic transvenous lead systems posesignificant management problems. Additionally, with the use of standardtransvenous ICDs in children, problems develop during patient growth inthat the lead system does not accommodate the growth. FIG. 9 illustratesthe placement of the S-ICD subcutaneous lead system such that he problemthat growth presents to the lead system is overcome. The distal end ofthe subcutaneous electrode is placed in the same location as describedabove providing a good location for the coilcardioversion/defibrillation electrode 27 and the sensing electrodes 23and 25. The insulated lead 21, however is no longer placed in a taughtconfiguration. Instead, the lead is serpiginously placed with aspecially designed introducer trocar and sheath such that it hasnumerous waves or bends. As the child grows, the waves or bends willstraighten out lengthening the lead system while maintaining properelectrode placement. Although it is expected that fibrous scarringespecially around the defibrillation coil will help anchor it intoposition to maintain its posterior position during growth, a lead systemwith a distal tine or screw electrode anchoring system 52 can also beincorporated into the distal tip of the lead to facilitate leadstability (see FIG. 1). Other anchoring systems can also be used such ashooks, sutures, or the like.

FIGS. 10 and 11 illustrate another embodiment of the present S-ICDinvention. In this embodiment there are two subcutaneous electrodes 13and 13′ of opposite polarity to the canister. The additionalsubcutaneous electrode 13′ is essentially identical to the previouslydescribed electrode. In this embodiment the cardioversion/defibrillationenergy is delivered between the active surface of the canister and thetwo coil electrodes 27 and 27′. Additionally, provided in the canisteris means for selecting the optimum sensing arrangement between the foursense electrodes 23, 23′, 25, and 25′. The two electrodes aresubcutaneously placed on the same side of the heart. As illustrated inFIG. 6, one subcutaneous electrode 13 is placed inferiorly and the otherelectrode 13′ is placed superiorly. It is also contemplated with thisdual subcutaneous electrode system that the canister and onesubcutaneous electrode are the same polarity and the other subcutaneouselectrode is the opposite polarity.

Turning now to FIGS. 12 and 13, further embodiments are illustratedwhere the canister 11 of the S-ICD of the present invention is shaped tobe particularly useful in placing subcutaneously adjacent and parallelto a rib of a patient. The canister is long, thin, and curved to conformto the shape of the patient's rib. In the embodiment illustrated in FIG.12, the canister has a diameter ranging from about 0.5 cm to about 2 cmwithout 1 cm being presently preferred. Alternatively, instead of havinga circular cross sectional area, the canister could have a rectangularor square cross sectional area as illustrated in FIG. 13 without fallingoutside of the scope of the present invention. The length of thecanister can vary depending on the size of the patient's thorax.Currently the canister is about 5 cm to about 15 cm long with about 10being presently preferred. The canister is curved to conform to thecurvature of the ribs of the thorax. The radius of the curvature willvary depending on the size of the patient, with smaller radiuses forsmaller patients and larger radiuses for larger patients. The radius ofthe curvature can range from about 5 cm to about 35 cm depending on thesize of the patient. Additionally, the radius of the curvature need notbe uniform throughout the canister such that it can be shaped closer tothe shape of the ribs. The canister has an active surface, 15 that islocated on the interior (concave) portion of the curvature and aninactive surface 16 that is located on the exterior (convex) portion ofthe curvature. The leads of these embodiments, which are not illustratedexcept for the attachment port 19 and the proximal end of the lead 21,can be any of the leads previously described above, with the leadillustrated in FIG. 1 being presently preferred.

The circuitry of this canister is similar to the circuitry describedabove. Additionally, the canister can optionally have at least one senseelectrode located on either the active surface of the inactive surfaceand the circuitry within the canister can be programmable as describedabove to allow for the selection of the best sense electrodes. It ispresently preferred that the canister have two sense electrodes 26 and28 located on the inactive surface of the canisters as illustrated,where the electrodes are spaced from about 1 to about 10 cm apart with aspacing of about 3 cm being presently preferred. However, the senseelectrodes can be located on the active surface as described above.

It is envisioned that the embodiment of FIG. 12 will be subcutaneouslyimplanted adjacent and parallel to the left anterior 5th rib, eitherbetween the 4th and 5th ribs or between the 5th and 6th ribs. Howeverother locations can be used.

Another component of the S-ICD of the present invention is a cutaneoustest electrode system designed to simulate the subcutaneous high voltageshock electrode system as well as the QRS cardiac rhythm detectionsystem. This test electrode system is comprised of a cutaneous patchelectrode of similar surface area and impedance to that of the S-ICDcanister itself together with a cutaneous strip electrode comprising adefibrillation strip as well as two button electrodes for sensing of theQRS. Several cutaneous strip electrodes are available to allow fortesting various bipole spacings to optimize signal detection comparableto the implantable system.

FIGS. 14 to 18 depict particular US-ICD embodiments of the presentinvention. The various sensing, shocking and pacing circuitry, describedin detail above with respect to the S-ICD embodiments, may additionallybe incorporated into the following US-ICD embodiments. Furthermore,particular aspects of any individual S-ICD embodiment discussed above,may be incorporated, in whole or in part, into the US-ICD embodimentsdepicted in the following figures.

Turning now to FIG. 14, the US-ICD of the present invention isillustrated. The US-ICD consists of a curved housing 1211 with a firstand second end. The first end 1413 is thicker than the second end 1215.This thicker area houses a battery supply, capacitor and operationalcircuitry for the US-ICD. The circuitry will be able to monitor cardiacrhythms for tachycardia and fibrillation, and if detected, will initiatecharging the capacitor and then delivering cardioversion/defibrillationenergy through the two cardioversion/defibrillating electrodes 1417 and1219 located on the outer surface of the two ends of the housing. Thecircuitry can provide cardioversion/defibrillation energy in differenttypes of waveforms. In one embodiment, a 100 uF biphasic waveform isused of approximately 10-20 ms total duration and with the initial phasecontaining approximately ⅔ of the energy, however, any type of waveformcan be utilized such as monophasic, biphasic, multiphasic or alternativewaveforms as is known in the art.

The housing of the present invention can be made out of titanium alloyor other presently preferred ICD designs. It is contemplated that thehousing is also made out of biocompatible plastic materials thatelectronically insulate the electrodes from each other. However, it iscontemplated that a malleable canister that can conform to the curvatureof the patient's chest will be preferred. In this way the patient canhave a comfortable canister that conforms to the unique shape of thepatient's rib cage. Examples of conforming ICD housings are provided inU.S. Pat. No. 5,645,586, the entire disclosure of which is hereinincorporated by reference. In the preferred embodiment, the housing iscurved in the shape of a 5th rib of a person. Because there are manydifferent sizes of people, the housing will come in differentincremental sizes to allow a good match between the size of the rib cageand the size of the US-ICD. The length of the US-ICD will range fromabout 15 to about 50 cm. Because of the primary preventative role of thetherapy and the need to reach energies over 40 Joules, a feature of thepreferred embodiment is that the charge time for the therapy,intentionally be relatively long to allow capacitor charging within thelimitations of device size.

The thick end of the housing is currently needed to allow for theplacement of the battery supply, operational circuitry, and capacitors.It is contemplated that the thick end will be about 0.5 cm to about 2 cmwide with about 1 cm being presently preferred. As microtechnologyadvances, the thickness of the housing will become smaller.

The two cardioversion/defibrillation electrodes on the housing are usedfor delivering the high voltage cardioversion/defibrillation energyacross the heart. In the preferred embodiment, thecardioversion/defibrillation electrodes are coil electrodes, however,other cardioversion/defibrillation electrodes could be used such ashaving electrically isolated active surfaces or platinum alloyelectrodes. The coil cardioversion/defibrillation electrodes are about5-10 cm in length. Located on the housing between the twocardioversion/defibrillation electrodes are two sense electrodes 1425and 1427. The sense electrodes are spaced far enough apart to be able tohave good QRS detection. This spacing can range from 1 to 10 cm with 4cm being presently preferred. The electrodes may or may not becircumferential with the preferred embodiment. Having the electrodesnon-circumferential and positioned outward, toward the skin surface, isa means to minimize muscle artifact and enhance QRS signal quality. Thesensing electrodes are electrically isolated from thecardioversion/defibrillation electrode via insulating areas 1423.Analogous types of cardioversion/defibrillation electrodes are currentlycommercially available in a transvenous configuration. For example, U.S.Pat. No. 5,534,022, the entire disclosure of which is hereinincorporated by reference, discloses a composite electrode with a coilcardioversion/defibrillation electrode and sense electrodes.Modifications to this arrangement is contemplated within the scope ofthe invention. One such modification is to have the sense electrodes atthe two ends of the housing and have the cardioversion/defibrillationelectrodes located in between the sense electrodes. Another modificationis to have three or more sense electrodes spaced throughout the housingand allow for the selection of the two best sensing electrodes. If threeor more sensing electrodes are used, then the ability to change whichelectrodes are used for sensing would be a programmable feature of theUS-ICD to adapt to changes in the patient physiology and size over time.The programming could be done via the use of physical switches on thecanister, or as presently preferred, via the use of a programming wandor via a wireless connection to program the circuitry within thecanister.

Turning now to FIG. 15, the optimal subcutaneous placement of the US-ICDof the present invention is illustrated. As would be evident to a personskilled in the art, the actual location of the US-ICD is in asubcutaneous space that is developed during the implantation process.The heart is not exposed during this process and the heart isschematically illustrated in the figures only for help in understandingwhere the device and its various electrodes are three dimensionallylocated in the thorax of the patient. The US-ICD is located between theleft mid-clavicular line approximately at the level of the inframammarycrease at approximately the 5^(th) rib and the posterior axillary line,ideally just lateral to the left scapula. This way the US-ICD provides areasonably good pathway for current delivery to the majority of theventricular myocardium.

FIG. 16 schematically illustrates the method for implanting the US-ICDof the present invention. An incision 1631 is made in the left anterioraxillary line approximately at the level of the cardiac apex. Asubcutaneous pathway is then created that extends posteriorly to allowplacement of the US-ICD. The incision can be anywhere on the thoraxdeemed reasonable by the implanting physician although in the preferredembodiment, the US-ICD of the present invention will be applied in thisregion. The subcutaneous pathway is created medially to the inframammarycrease and extends posteriorly to the left posterior axillary line. Thepathway is developed with a specially designed curved introducer 1742(see FIG. 17). The trocar has a proximal handle 1641 and a curved shaft1643. The distal end 1745 of the trocar is tapered to allow fordissection of a subcutaneous path in the patient. Preferably, the trocaris cannulated having a central lumen 1746 and terminating in an opening1748 at the distal end. Local anesthetic such as lidocaine can bedelivered, if necessary, through the lumen or through a curved andelongated needle designed to anesthetize the path to be used for trocarinsertion should general anesthesia not be employed. Once thesubcutaneous pathway is developed, the US-ICD is implanted in thesubcutaneous space, the skin incision is closed using standardtechniques.

As described previously, the US-ICDs of the present invention vary inlength and curvature. The US-ICDs are provided in incremental sizes forsubcutaneous implantation in different sized patients. Turning now toFIG. 18, a different embodiment is schematically illustrated in explodedview which provides different sized US-ICDs that are easier tomanufacture. The different sized US-ICDs will all have the same sizedand shaped thick end 1413. The thick end is hollow inside allowing forthe insertion of a core operational member 1853. The core membercomprises a housing 1857 which contains the battery supply, capacitorand operational circuitry for the US-ICD. The proximal end of the coremember has a plurality of electronic plug connectors. Plug connectors1861 and 1863 are electronically connected to the sense electrodes viapressure fit connectors (not illustrated) inside the thick end which arestandard in the art. Plug connectors 1865 and 1867 are alsoelectronically connected to the cardioverter/defibrillator electrodesvia pressure fit connectors inside the thick end. The distal end of thecore member comprises an end cap 1855, and a ribbed fitting 1859 whichcreates a water-tight seal when the core member is inserted into opening1851 of the thick end of the US-ICD.

The core member of the different sized and shaped US-ICD will all be thesame size and shape. That way, during an implantation procedures,multiple sized US-ICDs can be available for implantation, each onewithout a core member. Once the implantation procedure is beingperformed, then the correct sized US-ICD can be selected and the coremember can be inserted into the US-ICD and then programmed as describedabove. Another advantage of this configuration is when the batterywithin the core member needs replacing it can be done without removingthe entire US-ICD.

A block diagram of a power supply 100 for use in a S-ICD device of thepresent invention is shown in FIG. 19. The power supply 100 is locatedin canister housing 16 and comprises a capacitor subsystem 102electrically coupled to a battery subsystem 104. In an embodiment, thebattery subsystem 104 comprises one or more individual battery cell(s)and the capacitor subsystem 102 comprises one or more individualcapacitor(s).

In certain embodiments of the present invention, it is desirable toposition the canister housing 16 in close proximity to the patient'sheart, without directly contacting the heart or the intrathoracic bloodvessels. In one embodiment, the canister housing 16 placement is justover the patient's ribcage.

In operation, the battery subsystem 104 provides electrical energy tocharge up the capacitor subsystem 102. After charge-up, the capacitorsubsystem 102 delivers the cardioversion/defibrillation energy to thepatient's heart through the electrodes. In one embodiment, the powersupply 100 can provide approximately 0.5 to approximately 350 joules ofcardioversion/defibrillation energy to the heart through approximately60 ohms of thoracic impedance.

A procedure to determine the composition of the capacitor subsystem 102and the battery subsystem 104 will now be described. Generally, theapproach to determine needed capacitor values includes considerationsfor the internal impedance of the capacitors. As a result of thisinternal impedance, not all of the energy stored by the capacitors willbe delivered due to the inherent inefficiencies of the capacitors. Thus,it is often necessary to work backwards from the desired energydelivered in order to calculate the needed capacitor values.

Generally, the procedure to determine the proper capacitor values of thepresent invention includes the following steps: determine the amount ofcardioversion/defibrillation energy required to be delivered to thepatient's heart; determine the amount of energy lost due to truncationof the energy wave form; determine the amount of energy that must bestored in the capacitor subsystem 102 by considering the amount ofenergy loss from the internal impedance of the capacitor subsystem 102;determine the effective capacitor value of the capacitor subsystem 102associated with using different amounts of individual capacitors;calculate the physical volume of the different numbers of individualcapacitors for placement on a circuit board; and determine the pulsewidth for each of the effective capacitor values.

The first step is to determine the amount of energy that must bedelivered to a patient's heart to provide an effectivecardioversion/defibrillation therapy. In addition, the effective energylevels incorporate critical information regarding the associatedvoltage, current, waveform duration and tilt for effectivecardioversion/defibrillation. Use of the term “energy” throughout thisdescription automatically incorporates these other waveformcharacteristics. Because this information has not been availableheretofore, this data can be acquired by performing, for example, humanor animal studies to determine the appropriate levels of the energy.

Next, it is common industry practice to truncate the trailing edge of acapacitor-based cardioversion/defibrillation waveform because thetrailing edge can often produce undesirable side affects, such ascreating pro-arrhythmic currents should it persist too long. Thus, theamount of energy delivered can be calculated by the formula:E _(STORED) =E _(DEL) /T,where E_(STORED) is the maximum amount of energy by the capacitor,E_(DEL) is the amount of energy delivered to the heart and T is thetruncation percentage of the waveform.

In order to determine the amount of energy as shown above, the amount ofenergy stored in the capacitors is typically compensated for byconsidering the internal impedance of the capacitor subsystem 102, whichis known as the Effective Series Resistance (“ESR”). In addition, theratio of delivered energy to stored energy is often expressed as thecapacitor efficiency.

After calculation of the energy stored by the capacitor subsystem 102,the actual values of the individual capacitor(s) can be determined. Theamount of energy stored by an individual capacitor is given by theformula:E=½[C(V)²],where E is the total amount of energy stored by a capacitor, C is theamount of capacitance and V is the amount of voltage for each individualcapacitor. From this equation, it can be seen that a number of tradeoffsexist in determining the capacitor value(s) to achieve the desiredcardioversion/defibrillation output, including the individual capacitorvalue(s) and the voltage across each individual capacitor(s). Forexample, considerations may include voltages of commercially availablecapacitors as well as specific capacitor values most appropriate forcardioversion/defibrillation therapy.

It is also noted from the equation above that larger voltages permitsmaller values of capacitors in order to obtain the same energy level.The voltage is constrained, however, by the voltage limitation of eachindividual capacitor. Often, in order to produce voltages required forcardioversion/defibrillation, a series connection of capacitors may beimplemented to allow these higher overall output voltages, while at thesame time keeping each individual capacitors' voltage below its maximumrating. Examples of embodiments of the present invention whenconsidering these factors are shown in greater detail below.

Typically, the value for each individual capacitor, C_(IND) isdetermined first for the capacitor subsystem 102. Next, the effectivecapacitance of the capacitor subsystem 102, C_(EFF), can be determinedfrom the equation above. Solving for C_(EFF), the equation above becomesC_(EFF)=2×E/(V)².

Finally, once the individual capacitor value(s) have been determined,the physical volume for each of the individual capacitor(s) can also bedetermined. In order to solve for volume of the individual capacitors,the equation is used as follows:V _(IND) =E/volumetric density,where V_(IND) is the individual capacitor volume, E is the storedenergy, and the volumetric density is measured in joules/cubiccentimeters. Under multiple capacitor scenarios, individual capacitorvolumes can be summed to determine the total volume due to thecapacitors. Specifically, the total device volume can be determined bythe equation E_(TOTAL)=(the number of capacitors)×V_(IND).

Derivation of the equation used to determine pulse width depends on theamount of cardioversion/defibrillation energy delivered by the capacitorsubsystem 102. In addition, the pulse width must be truncated or thepulse width will stretch indefinitely because of the exponential natureof the components. Specifically, the amount of energy delivered by thecapacitor subsystem 102 can be determined by the fact that the amount ofenergy left in the capacitor subsystem 102, E_(FINAL), is equal to theamount of the energy initially stored in the capacitor subsystem 102,E_(INIT), minus the amount of energy delivered by the shock, E_(DEL). Inaddition, the amount of energy stored in the capacitor subsystem 102after a shock, E_(FINAL), is also defined by the equation as follows:E_(FINAL)=½[C _(Eff) ][V _(FINAL)]²=½[C _(EFF) ][V _(INIT) ]e ^(−τ/RC)_(EFF)]²,where τ is the pulse width and R is the impedance of the body.

After calculating the makeup of the capacitor subsystem 104, thecomposition of the battery subsystem 102 of the present invention can bedetermined. First, the total amount of energy for the battery subsystem104 that is required to provide a maximum number of energy shocks at acertain amount of energy delivered is determined. Next, afterconsidering th e overall efficiency of the battery subsystem 102, thetotal amount of energy for this number of energy shocks is calculated.Finally , the total physical volume and effective lifetime of thebattery subsystem 102 can be determined.

Based on the calculations described above, several examples ofembodiments of the capacitor subsystem 102 and the battery subsystem 104will now be shown. As an example of an embodiment of the presentinvention, the power supply 100 may provide approximately 150 joules ofenergy to be delivered to the heart. Further, in an embodiment, thewaveform of the energy delivered to the heart will be truncated atapproximately 97%. Therefore, in this example, the energy output of thecapacitor, E_(OUT), will equal to 150 joules divided by the truncationlevel 97%, or 155 joules.

In an embodiment, the efficiency of the energy stored in the capacitoris approximately 75%. With an energy output of the capacitor equal to155 joules, the stored energy will be 155 joules divided by theefficiency 75%, or 207 joules.

The effective capacitance C_(EFF) can now be calculated using theequation C_(EFF)=2×E/(V)². In this example, assuming E is approximately207 joules and V is approximately 350 volts, C_(EFF) is approximately3,380 microfarads. Because the individual capacitance, C_(IND), equalsthe number of capacitors times the effective capacitance, C_(EFF), theindividual capacitance of the single capacitor also is approximately3,380 microfarads.

In order to solve for physical volume, the equation V_(IND)=E/volumemetric density is used. In this example, it is assumed that theindividual capacitors have a volumetric efficiency of approximately 7.5joules/cubic centimeters for stored energy and approximately 5.5joules/cubic centimeters for delivered energy. Therefore, in thisexample, individual capacitor volume, V_(IND)=207 joules/7.5joules/cubic centimeters=27.6 cubic centimeters. Further, because thecapacitor volume is determined by the number of capacitors timesV_(IND), in this example with one individual capacitor, the totalcapacitor device, V_(TOT)=27.6 cubic centimeters.

Finally, the value of the pulse width can be determined. In thisexample, E_(FINAL)=E_(INIT)−E_(DEL)=155.0-150.0=5.0 joules. In addition,using the equationE_(FINAL)=½[C_(Eff)][V_(FINAL)]²=½[C_(EFF)][V_(INIT)][e^(−τ/RC)_(EFF)]², the pulse width τ is equal to 377 milliseconds.

As shown in the table in FIG. 20, several examples of embodiments of thepower supply 100 of the present invention are shown to depending uponthe number of capacitors and the pulse width of the energy signaldelivered. In addition, FIG. 21 shows in graphical form the tabular datashown in FIG. 20.

Next, it is desired to determine the size of the battery subsystem 104is required given a maximum number of energy shocks at a certain amountof energy delivered. In this example, it is assumed that the system iscapable of delivering approximately 100 maximum energy shocks atapproximately 207 joules of energy. Accordingly, because 207 joules ofenergy is equal to 207 watt-seconds, 100 max energy shocks is equal to20,700 watt-seconds, or 5.75 watt-hours. Assuming for this example thatthe power supply efficiency is approximately 65%, this yields a batterycapacity requirement of 8.8 watt-hours.

In one embodiment of the present invention, the battery cells cancomprise LiSVO or LiMnO₂ batteries that can operate for bothdefibrillation or monitoring requirements. In another embodiment, LiSVOor LiMnO₂ batteries can be employed for defibrillation operations, andLiI₂ or LiCFx batteries can be employed for monitoring operations.

In this example, the LiSVO batteries have a energy storage capacity ofapproximately ½ watt-hour/cubic centimeters per battery. Therefore, aphysical volume of approximately 18 cubic centimeters of battery isrequired to provide 100 maximum energy shocks at approximately 207joules of energy.

Another variable relates to time required for the battery subsystem 102to fully charge the capacitor subsystem 104. Because batteries tend todegrade over the life of the cells, the charge time at the beginning ofbattery life (“BOL”) is less than the end of the battery life (“EOL”).The amount of charge time is equal to the power output divided by theapplied battery voltage at the BOL times the maximum current. As anexample, assuming a single shock of approximately 207 joules at a 65%efficiency that yields a power output of approximately 318 joules, andan applied battery voltage of approximately 5 volts at BOL and maximumcurrent drain of approximately 2.5 amps, the battery subsystem 102 cancharge the capacitor subsystem 104 in approximately 25 seconds. In thisexample, assuming the applied battery voltage decrease to approximately4 volts at EOL with a current drain of approximately 2.5 amps, thebattery subsystem can charge the capacitor subsystem 104 inapproximately 32 seconds.

Finally, in order to determine the effective lifetime of the batterysubsystem 102 assuming no shocks and no pacing, the amount of batterycapacity (8.8 watt-hours) must be divided by the amount of monitoringcurrent (15 microamps) times the total voltage (10.0 volts) times thebattery efficiency (90%). For this example, the battery subsystem has aneffective lifetime of approximately 65,185 hours, or 7.4 years.

In an embodiment, commercially available capacitors and batteriesmeeting the specifications described above are manufactured and sold byWilson Greatbatch, Limited, of 10,000 Wehrle Dr., Clarence, N.Y. 14031.In an embodiment, the capacitor subsystem 104 can comprise film,aluminum electrolytic or wet tantalum capacitor(s). In an embodiment,the battery subsystem can comprise LiSVO, magnesium or thin filmbattery(ies).

FIG. 22 is a table that shows several examples for the battery subsystem102 comprising two battery cells, as well as varying efficiencies andcharge times. In addition, FIG. 23 is a table that shows severalexamples for the battery subsystem 102 comprising other numbers ofbattery cells, efficiencies and charge times.

FIG. 24 is a diagram that shows one example of a physical layout for thebattery subsystem 102 and the capacitor subsystem 104 in an embodimentof the present invention. As shown in FIG. 24, battery subsystem 102 maycomprise battery cells 2402, 2404, 2406 and 2408. Capacitor subsystem104 may comprise capacitors 2410, 2412, 2414, 2416, 2418 and 2420. Boththe battery subsystem 102 and the capacitor subsystem 104 are located inthe canister housing 16. In this example, it is assumed that thethickness 2424 of the canister housing 16 will be approximately 0.2inches. As determined in the example above, each of the six capacitors2410, 2412, 2414, 2416, 2418 and 2420 can occupy approximately 4.6 cubiccentimeters of physical volume. In this example, it is noted thatcapacitor 2410 is substantially a half-circle in shape. Because volumeis equal to area times thickness 2424 and assuming the device is 0.2inches thick, the radius 2422 of the half-circle capacitor 16 isapproximately 0.95 inches. Next, because the width 2426 is equal totwice the radius 2422, the width 2426 is approximately 1.9 inches. Then,assuming the width 2426 is approximately 1.9 inches, the thickness 2424is approximately 0.2 inches and the volume of each of the capacitors2412, 2414, 2416, 2418 and 2420 is approximately 4.6 cubic centimeters,each of the individual capacitors is approximately 0.74 inches inlength. Therefore, the capacitor subsystem 104 is approximately 4.6inches in length.

As for the battery subsystem 102, assuming approximately 4.5 cubiccentimeters of volume per battery, the same width 2426 and thickness2424, the length of each of the battery cells 2402, 2404, 2406 and 2408is approximately 0.72 inches for a total of approximately 2.9 inches.Thus, the length 2428 of the canister housing 16 is approximately 4.6inches (capacitor subsystem 104) plus 2.9 inches (battery subsystem 102)or a total of approximately 7.5 inches. Similarly, multiplying thelength 2428 times the width 2426 times the thickness 2424 provides atotal volume in this example of approximately 50 cubic centimetersincluding a provision for the electronics.

FIG. 25 shows one example of a physical layout for the battery subsystem102 and the capacitor subsystem 104 in an embodiment of the presentinvention. As shown in FIG. 25, battery subsystem 102 may comprisebattery cells 2502, 2504, 2506 and 2508. Capacitor subsystem 104 maycomprise capacitors 2510, 2512, 2514, 2516, 2518 and 2520. Both thebattery subsystem 102 and the capacitor subsystem 104 are located in thecanister housing 16. In this example, it is assumed that thickness 2524of the canister housing 16 is approximately 0.3 inches. As determined inthe example above, each of the six capacitors 2510, 2512, 2514, 2516,2518 and 2520 will occupy approximately 4.6 cubic centimeters ofphysical volume. Assuming a width 2526 of approximately 2.0 inches, thelength of each of the capacitors 2510, 2512, 2514, 2516, 2518 and 2520is approximately 0.47 inches, and the total length of the capacitorsubsystem 104 is approximately 2.8 inches. Next, given the sameassumptions for the thickness 2524 and the width 2526, and that thevolume of each of the battery cells 2502, 2504, 2506 and 2508 isapproximately 4.5 cubic centimeters (as calculated above), each of thebattery cells 2502, 2504, 2506 and 2508 is approximately 0.46 inches.Thus, the length of the battery subsystem 102 is approximately 1.8inches and the length 2528 of the combined capacitor subsystem 104 andthe battery subsystem 102 is approximately 2.8 inches plus 1.8 inches,or 4.6 inches. Further, the total volume of the capacitor subsystem 104and the battery subsystem 102 is approximately 50 cubic centimeters.

FIG. 26 shows a table with various examples of sizes for the combinedcapacitor subsystem 104 and the battery subsystem 102. Morespecifically, the table shows various thicknesses, widths and lengths,and which all have the same volume of approximately 50 cubiccentimeters. There are, of course, many variations to these potentialembodiments shown in FIG. 26.

Finally, FIG. 27 shows a table of several embodiments of the capacitorsubsystem 104 and the battery subsystem 102 at different energy levels.In these examples, energy levels of 150, 125, 100, 75 and 50 joules areshown. Typically, the amount of delivered energy can range fromapproximately 0.5 joules to approximately 350 joules. Also, in anembodiment, the peak voltage of the energy can range from approximately350 volts to approximately 3150 volts. In addition, in these examples, anominal effective capacitance of 100 microfarads is targeted to alignwith defibrillation chronaxie.

The S-ICD and US-ICD devices and methods of the present invention may beembodied in other specific forms without departing from the teachings oressential characteristics of the invention. The described embodimentsare therefore to be considered in all respects as illustrative and notrestrictive, the scope of the invention being indicated by the appendedclaims rather than by the foregoing description, and all changes whichcome within the meaning and range of equivalency of the claims aretherefore to be embraced therein.

1. A power supply for an implantable cardioverter-defibrillator forsubcutaneous positioning between the third rib and the twelfth rib andfor providing cardioversion/defibrillation energy to the heart, thepower supply comprising: a capacitor subsystem for storing thecardioversion/defibrillation energy for delivery to the patient's heart;and a battery subsystem electrically coupled to the capacitor subsystemfor providing electrical energy to the capacitor subsystem.
 2. The powersupply of claim 1 , wherein the cardioversion/defibrillation energy isapproximately 0.5 to approximately 350 joules.
 3. The power supply ofclaim 2, wherein the cardioversion/defibrillation energy isapproximately 0.5 to approximately 20 joules.
 4. The power supply ofclaim 2, wherein the cardioversion/defibrillation energy isapproximately 20 to approximately 40 joules.
 5. The power supply ofclaim 2, wherein the cardioversion/defibrillation energy isapproximately 210 to approximately 250 joules.
 6. The power supply ofclaim 2, wherein the cardioversion/defibrillation energy isapproximately 250 to approximately 300 joules.
 7. The power supply ofclaim 2, wherein the cardioversion/defibrillation energy isapproximately 300 to approximately 350 joules.
 8. The power supply ofclaim 1, wherein the capacitor subsystem has an effective capacitance ofapproximately 25 microfarads to approximately 200 microfarads.
 9. Thepower supply of claim 1, wherein the capacitor subsystem comprises oneor more film capacitor(s).
 10. The power supply of claim 1, wherein thecapacitor subsystem comprises one or more aluminum electrolyticcapacitor(s).
 11. The power supply of claim 1, wherein the capacitorsubsystem comprises one or more wet tantalum capacitor(s).
 12. The powersupply of claim 1, wherein the battery subsystem comprises one or moreLiSVO battery(ies).
 13. The power supply of claim 1, wherein the batterysubsystem comprises one or more LiMnO₂ battery(ies).
 14. The powersupply of claim 1, wherein the battery subsystem comprises one or moreLiI₂ battery(ies).
 15. The power supply of claim 1, wherein the batterysubsystem comprises one or more LICF_(x) battery(ies).
 16. The powersupply of claim 1, wherein the battery subsystem comprises one or morethin film battery(ies).
 17. A power supply for an implantablecardioverter-defibrillator for subcutaneous positioning outside theribcage and between the third rib and the twelfth rib within a patientand using a lead system that does not directly contact the patient'sheart or reside in the intrathoracic blood vessels, and for providingcardioversion/defibrillation energy to the heart, the power supplycomprising: a capacitor subsystem for storing thecardioversion/defibrillation energy for delivery to the patient's heart;and a battery subsystem electrically coupled to the capacitor subsystemfor providing electrical energy to the capacitor subsystem.
 18. Thepower supply of claim 17, wherein the cardioversion/defibrillationenergy is approximately 0.5 to approximately 350 joules.
 19. The powersupply of claim 18, wherein the cardioversion/defibrillation energy isapproximately 0.5 to approximately 20 joules.
 20. The power supply ofclaim 18, wherein the cardioversion/defibrillation energy isapproximately 20 to approximately 40 joules.
 21. The power supply ofclaim 18, wherein the cardioversion/defibrillation energy isapproximately 210 to approximately 250 joules.
 22. The power supply ofclaim 18, wherein the cardioversion/defibrillation energy ofapproximately 250 to approximately 300 joules.
 23. The power supply ofclaim 18, wherein the cardioversion/defibrillation energy isapproximately 300 to approximately 350 joules.
 24. The power supply ofclaim 17, wherein the capacitor subsystem has an effective capacitanceof approximately 25 microfarads to approximately 200 microfarads. 25.The power supply of claim 17, wherein the capacitor subsystem comprisesone or more film capacitor(s).
 26. The power supply of claim 17, whereinthe capacitor subsystem comprises one or more aluminum electrolyticcapacitor(s).
 27. The power supply of claim 17, wherein the capacitorsubsystem comprises one or more wet tantalum capacitor(s).
 28. The powersupply of claim 17, wherein the battery subsystem comprises one or moreLiSVO battery(ies).
 29. The power supply of claim 17, wherein thebattery subsystem comprises one or more LiMnO₂ battery(ies).
 30. Thepower supply of claim 17, wherein the battery subsystem comprises one ormore LiI₂ battery(ies).
 31. The power supply of claim 17, wherein thebattery subsystem comprises one or more LiCF_(x) battery(ies).
 32. Thepower supply of claim 17, wherein the battery subsystem comprises one ormore thin film battery(ies).
 33. A voltage output system for animplantable heart stimulator for subcutaneous positioning between thethird rib and the twelfth rib within a patient and employing a leadsystem that does not directly contact the patient's heart or reside inthe intrathoracic blood vessels, comprising: an energy storage systemfor storing electrical energy to generate an electrical stimulationpulse for delivery to the patient's heart; and an energy source systemoperably connected to the energy storage system for providing theelectrical energy to the energy storage system.
 34. The voltage outputsystem of claim 33, wherein the electrical stimulation pulse isapproximately 40 to approximately 210 joules.
 35. The voltage outputsystem of claim 34, wherein the electrical stimulation pulse isapproximately 0.5 to approximately 20 joules.
 36. The voltage outputsystem of claim 34, wherein the electrical stimulation pulse isapproximately 20 to approximately 40 joules.
 37. The voltage outputsystem of claim 34, wherein the electrical stimulation pulse isapproximately 210 to approximately 250 joules.
 38. The voltage outputsystem of claim 34, wherein the electrical stimulation pulse isapproximately 250 to approximately 300 joules.
 39. The voltage outputsystem of claim 34, wherein the electrical stimulation pulse isapproximately 300 to approximately 350 joules.
 40. The voltage outputsystem of claim 34, wherein the energy storage system has an effectivecapacitance of approximately 25 microfarads to approximately 200microfarads.
 41. The voltage output system of claim 33, wherein thecapacitor subsystem comprises one or more film capacitor(s).
 42. Thevoltage output system of claim 33, wherein the capacitor subsystemcomprises one or more aluminum electrolytic capacitors(s).
 43. Thevoltage output system of claim 33, wherein the capacitor subsystemcomprises one or more wet tantalum capacitor(s).
 44. The voltage outputsystem of claim 33, wherein the battery subsystem comprises one or moreLiSVO battery(ies).
 45. The voltage output system of claim 33, whereinthe battery subsystem comprises one or more LiMnO₂ battery(ies).
 46. Thevoltage output system of claim 33, wherein the battery subsystemcomprises one or more LiI₂ battery(ies).
 47. The voltage output systemof claim 33, wherein the battery subsystem comprises one or moreLiCF_(x) battery(ies).
 48. The voltage output system of claim 33,wherein the battery subsystem comprises one or more thin filmbattery(ies).
 49. An implantable cardioverter-defibrillator forsubcutaneous positioning outside the ribcage and between the third riband the twelfth rib within a patient, the implantablecardioverter-defibrillator comprising: a housing having an electricallyconductive surface on an outer surface of the housing; a lead assemblyelectrically coupled to the housing and having an electrode, wherein thelead assembly does not directly contact the patient's heart or reside inthe intrathoracic blood vessels; a capacitor subsystem located withinthe housing and electrically coupled to the electrically conductivesurface and the electrode for storing cardioversion/defibrillationenergy and for delivering the cardioversion/defibrillation energy to thepatient's heart through the electrically conductive surface and theelectrode; and a battery subsystem electrically coupled to the capacitorsubsystem for providing the cardioversion/defibrillation energy to thecapacitor subsystem.
 50. The implantable cardioverter-defibrillator ofclaim 49, wherein the cardioversion/defibrillation energy isapproximately 0.5 to approximately 350 joules.
 51. The implantablecardioverter-defibrillator of claim 50, wherein thecardioversion/defibrillation energy is approximately 0.5 toapproximately 20 joules.
 52. The implantable cardioverter-defibrillatorof claim 50, wherein the cardioversion/defibrillation energy isapproximately 20 to approximately 40 joules.
 53. The implantablecardioverter-defibrillator of claim 50, wherein thecardioversion/defibrillation energy is approximately 210 toapproximately 250 joules.
 54. The implantable cardioverter-defibrillatorof claim 50, wherein the cardioversion/defibrillation energy ofapproximately 250 to approximately 300 joules.
 55. The implantablecardioverter-defibrillator of claim 50, wherein thecardioversion/defibrillation energy is approximately 300 toapproximately 350 joules.
 56. The implantable cardioverter-defibrillatorof claim 50, wherein the capacitor subsystem has an effectivecapacitance of approximately 25 microfarads to approximately 200microfarads.
 57. The implantable cardioverter-defibrillator of claim 49,wherein the capacitor subsystem comprises one or more film capacitor(s).58. The implantable cardioverter-defibrillator of claim 49, wherein thecapacitor subsystem comprises one or more aluminum electrolyticcapacitor(s).
 59. The implantable cardioverter-defibrillator of claim49, wherein the capacitor subsystem comprises one or more wet tantalumcapacitor(s).
 60. The implantable cardioverter-defibrillator of claim49, wherein the battery subsystem comprises one or more LiSVObattery(ies).
 61. The implantable cardioverter-defibrillator of claim49, wherein the battery subsystem comprises one or more LiMnO₂battery(ies).
 62. The implantable cardioverter-defibrillator of claim49, wherein the battery subsystem comprises one or more LiI₂battery(ies).
 63. The implantable cardioverter-defibrillator of claim49, wherein the battery subsystem comprises one or more LiCF_(x)battery(ies).
 64. The implantable cardioverter-defibrillator of claim49, wherein the battery subsystem comprises one or more thin filmbattery(ies).
 65. A method of supplying power for an implantablecardioverter-defibrillator for subcutaneous positioning outside theribcage and between the third rib and the twelfth rib within a patientand using a lead system that does not directly contact the patient'sheart or reside in the intrathoracic blood vessels, the methodcomprising: generating cardioversion/defibrillation energy; storing thecardioversion/defibrillation energy; and delivering thecardioversion/defibrillation energy to the patient's heart.
 66. Themethod of claim 65, wherein the cardioversion/defibrillation energy isapproximately 0.5 to approximately 350 joules.
 67. The method of claim66, wherein the cardioversion/defibrillation energy is approximately 0.5to approximately 20 joules.
 68. The method of claim 66, wherein thecardioversion/defibrillation energy is approximately 20 to approximately40 joules.
 69. The method of claim 66, wherein thecardioversion/defibrillation energy is approximately 210 toapproximately 250 joules.
 70. The method of claim 66, wherein thecardioversion/defibrillation energy of approximately 250 toapproximately 300 joules.
 71. The method of claim 66, wherein thecardioversion/defibrillation energy is approximately 300 toapproximately 350 joules.
 72. The method of claim 65, wherein the energystorage system has an effective capacitance of approximately 25microfarads to approximately 200 microfarads.
 73. The method of claim65, wherein the capacitor subsystem comprises one or more filmcapacitor(s).
 74. The method of claim 65, wherein the capacitorsubsystem comprises one or more aluminum electrolytic capacitor(s). 75.The method of claim 65, wherein the capacitor subsystem comprises one ormore wet tantalum capacitor(s).
 76. The method of claim 65, wherein thebattery subsystem comprises one or more LiSVO battery(ies).
 77. Themethod of claim 65, wherein the battery subsystem comprises one or moreLiMnO₂ battery(ies).
 78. The method of claim 65, wherein the batterysubsystem comprises one or more LiI₂ battery(ies).
 79. The method ofclaim 65, wherein the battery subsystem comprises one or more LiCF_(x)battery(ies).
 80. The method of claim 65, wherein the battery subsystemcomprises one or more thin film battery(ies).
 81. A power supply for animplantable cardioverter-defibrillator for subcutaneous positioningoutside the ribcage and between the third rib and the twelfth rib withina patient and using a lead system that does not directly contact thepatient's heart or resided in the intrathoracic blood vessels, and forproviding cardioversion/defibrillation energy to the heart, the methodcomprising: means for storing the cardioversion/defibrillation energyand delivering the cardioversion/defibrillation energy to the patient'sheart; means for providing cardioversion/defibrillation energy to themeans for storing the cardioversion/defibrillation energy.
 82. The powersupply of claim 81, wherein the cardioversion/defibrillation energy isapproximately 0.5 to approximately 350 joules.
 83. The power supply ofclaim 82, wherein the cardioversion/defibrillation energy isapproximately 0.5 to approximately 20 joules.
 84. The power supply ofclaim 82, wherein the cardioversion/defibrillation energy isapproximately 20 to approximately 40 joules.
 85. The power supply ofclaim 82, wherein the cardioversion/defibrillation energy isapproximately 210 to approximately 250 joules.
 86. The power supply ofclaim 82, wherein the cardioversion/defibrillation energy ofapproximately 250 to approximately 300 joules.
 87. The power supply ofclaim 82, wherein the cardioversion/defibrillation energy isapproximately 300 to approximately 350 joules.
 88. The power supply ofclaim 81, wherein the means for storing the cardioversion/defibrillationenergy has an effective capacitance of approximately 25 microfarads toapproximately 200 microfarads.
 89. The power supply of claim 81, whereinthe capacitor subsystem comprises one or more film capacitor(s).
 90. Thepower supply of claim 81, wherein the capacitor subsystem comprises oneor more aluminum electrolytic capacitor(s).
 91. The power supply ofclaim 81, wherein the capacitor subsystem comprises one or more wettantalum capacitor(s).
 92. The power supply of claim 81, wherein thebattery subsystem comprises one or more LiSVO battery(ies).
 93. Thepower supply of claim 81, wherein the battery subsystem comprises one ormore LiMnO₂ battery(ies).
 94. The power supply of claim 81, wherein thebattery subsystem comprises one or more LiI₂ battery(ies).
 95. The powersupply of claim 81, wherein the battery subsystem comprises one or moreLiCF_(x) battery(ies).
 96. The power supply of claim 81, wherein thebattery subsystem comprises one or more thin film battery(ies).
 97. Thepower supply of claim 81, wherein the implantablecardioverter-defibrillator is positioned subcutaneously between thethird and fifth ribs.
 98. The power supply of claim 81, wherein theimplantable cardioverter-defibrillator is positioned subcutaneouslybetween the fourth and sixth ribs.
 99. The power supply of claim 81,wherein the implantable cardioverter-defibrillator is positionedsubcutaneously between the sixth and eighth ribs.
 100. The power supplyof claim 81, wherein the implantable cardioverter-defibrillator ispositioned subcutaneously between the eighth and tenth ribs.
 101. Thepower supply of claim 81, wherein the implantablecardioverter-defibrillator is positioned subcutaneously between thetenth and twelfth ribs.
 102. The power supply of claim 81, wherein theimplantable cardioverter-defibrillator provides anti-tachycardia pacingenergy to the heart for treatment of atrial fibrillation.
 103. The powersupply of claim 81, wherein the implantable cardioverter-defibrillatorprovides anti-tachycardia pacing energy to the heart for treatment ofventricular tachycardia.